Regenerated collagen fibers are protein fibers that have highly characteristic structure derived from collagen, and their feel, gloss, and texture are quite similar to those of human hair, which is a natural protein fiber with sophisticated microstrucuture. For this reason, attempts have been made to use regenerated collagen fibers as fibers for artificial hair.
As raw materials of regenerated collagen fibers, animal skin and bones are generally used. Regenerated collagen fibers are produced by subjecting such raw materials to an alkali treatment or enzyme treatment to obtain water-soluble collagen, and then extruding the water-soluble collagen into an aqueous inorganic salt solution to spin the collagen into regenerated collagen fibers. However, regenerated collagen fibers obtained in such a manner are soluble in water, and thus have poor heat resistance. Therefore, in order to make the regenerated collagen fibers resistant to water and heat, they are treated to be insoluble in water.
As ways to make the regenerated collagen fibers insoluble in water in order to impart water resistance and heat resistance to the fibers, crosslinking the regenerated collagen fibers with aldehyde compounds such as formaldehyde or glutaraldehyde, epoxide compounds, or metal salts such as chrome salt, aluminum salt, or zirconium salt are known.
For example, Patent Document 1 suggests crosslinking regenerated collagen fibers with aldehyde compounds or polyfunctional epoxide compounds to improve water resistance. Patent document 2 suggests crosslinking regenerated collagen fibers with epihalohydrins or hydrogen halide adducts of epihalohydrins to make the fibers insoluble. Patent Document 3 suggests making regenerated collagen fibers water-insoluble using epoxide compounds or metal salts such as zirconium salts or aluminum salts.
Meanwhile, as to hair ornamental products using fibers for artificial hair, curls are given to the fibers by twisting, etc., to impart better styling properties.